I’m not the one asked, but since i am owner of an old ass myself i’ll chip in. My solution would be to reduce the desktop resolution if desktop readability is the problem. 4k is probably not the resolution you are gaming at? even if you do, you can just select a lower desktop resolution and crank it up when gaming (if the game supports scaling). other than that i can only recommend using magnification tools for the desktop and i don’t think there are any solutions for games that don’t bring their own scaling.

for my part, i use steams big picture mode as uion the tv, which works on any resolution.